In modern industrial processes using automatic and continuous food cooking machines, the foodstuff is heat treated on an endless belt. In a continuous food cooking machine a grilling or frying of food products is accomplished by placing them between parallel endless conveyor belts, where they are roasted. Furthermore, many flat food products are nowadays subjected to contact cooking in a device, in which they are squeezed or compressed between two surfaces.
After the heat treatment of the foodstuff the product has to be cooled for consumption or further conservation. In this connection cooling refers to a process wherein heat is removed from the product without the formation of ice.
In order to properly treat the foodstuff it is important to reduce the destruction processes in the food, which are microbiological, chemical, biochemical or physical. It is thus important that the foodstuff is rapidly cooled. This can be difficult since foodstuffs mostly are poor heat conductors, especially for products which have been heated above the critical temperature interval for microbial growth of 10-50.degree. C., an interval that has to be passed during the cooling procedure.
In one commonly used cooling method the foodstuff is after the heat treatment transported through a tunnel with circulating cold air. The heat transfer can be increased by increasing the speed of the air-flow, which together with the temperature of the air is adapted to the individual product.
When the food product is exposed to such an air-flow in an open atmosphere moisture will be lost, and there is a risk of the product being experienced as dry. These losses can amount to about 2-3% of the total weight of the product.
Furthermore, the evaporation and the condensation of the steam formed during such cooling processes can cause problems with the product when the cooling process is immediately followed by a freezing process. Then ice will be formed on the freezing elements. This reduces the capacity of the facility which then has to be repeatedly defrosted.
Apart from passing the critical temperature interval for microbial growth the food product is during the traditional cooling with air inevitably exposed to contaminating microorganisms if no extreme precautions are taken. These microorganisms can cause serious effects during the further handling of the food product.